This writeup is for a Jeep Cherokee XJ 97-01.
Be smart and replace both the heater core and the AC evaporator even if one is not needed. I even did the blower motor as well. Doing all three adds a total of about 1 minute to the job. Do you really want to do this again in the future?
Take a lot of pictures when disassembling. It will be very helpful when you go to put everything back together. Especially if you are splitting the job up between a few days.
Time needed: Roughly 10 hours for first timer.